US3440323A

US3440323A - Refractory crucibles

Info

Publication number: US3440323A
Application number: US563256A
Authority: US
Inventors: John Christie Howard
Original assignee: Associated Electrical Industries Ltd
Current assignee: Wellman Furnaces Ltd
Priority date: 1966-07-06
Filing date: 1966-07-06
Publication date: 1969-04-22
Anticipated expiration: 1986-04-22

Description

P 1969 J. c. HOWARD 7 3,440,323

REFRACTORY CRUCIBLE'S Filed July 6, 1966 Sheet of 2' April 2, 1969 J. c. HOWARD 3,440,323

REFRACTORY CRUCIBLES Filed July 6, 1966 Sheet 2 of 2 United States Patent 3,440,323 REFRACTORY CRUCIBLES John Christie Howard, Curbar, near Sheflield, England,

assignor to Associated Electrical Industries Limited,

London, England Filed July 6, 1966, Ser. No. 563,256 Int. Cl. H05b 5/14 US. CI. 13-30 16 Claims ABSTRACT OF THE DISCLOSURE In a furnace crucible of the kind having a duct which communicates with two spaced apart regions of the crucible and threads an annular magnetic core, the duct is formed by a plurality of parts each including an outer metal sheath and an inner refractory lining, the parts being releasably connected to each other and to the crucible so that the duct can be removed and replaced without dismantling the magnetic core.

This invention relates to refractory vessels such as crucibles and ladies and troughs or launders for containing a charge of molten metal and for use in or as, or in conjunction with a furnace capable of melting the metal charge and/or maintaining the charge in molten condition.

Such a refractory vessel generally comprises a main body portion capable of holding the main part of the charge and, except in the case of a trough or launder, a pouring spout or lip which is at an upper end of the crucible when the crucible is in a first normal upright position permitting no discharge of melt. The melt is discharged through the spout or over the lip when the crucible is tilted into a second pouring position.

In such a vessel it is essential to maintain the melt at a substantially constant temperature if discharge of the melt is to occur over a prolonged period, for example during controlled pouring of the melt into a plurality of casting moulds. In order to supply suflicient heat to the melt to maintain it at the desired temperature, the normally lower end of the vessel is provided with an extended portion which includes a substantially U-shaped duct having its opposite ends communicating with the inside of the body portion respectively at two spaced apart regions. When the vessel contains a molten metal charge, the metal in the duct and in the body portion forms a closed electrically conducting turn. Induction heating means, including an electric winding inductively coupled to the metal in the duct, effect induction heating of the metal in the duct and thereby of the metal in the remainder of the vessel, when suitably energised. The energisation of the winding can be adjusted to maintain the melt at the desired temperature.

With the vessel in use, the rate of erosion of the refractory material of the crucible is particularly high within the duct where the metal becomes induction heated. This rate of erosion becomes excessive in the case of iron, steel and other refractory erosive metals and necessitates frequent dismantling and rebuilding of the vessel.

According to the present invention, a refractory vessel for containing a charge of molten metal, comprises a main body portion capable of holding a substantial part of the charge and a duct having a refractory wall and which extends from the normally lower end of the body portion and which has its opposite ends communicating with the inside of the body portion respectively at two spaced apart regions thereof, the duct comprising at least one part consisting of an outer metal sheath and an inner refractory lining, the part or parts being releasably 3,440,323 Patented Apr. 22, 1969 connected to the vessel and in the case of a plurality of parts, to one another so as to permit the part or one or more of the parts to be readily replaced.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a side 'view of a metal pouring furnace including a refractory crucible; and

FIGURE 2 is a sectional view of the furnace shown in FIGURE 1, taken on the line II-II and looking in the direction indicated by the arrows.

Referring to the drawings, the furnace includes a substantially cylindrical crucible 2 comprising a suitable refractory lining 4 within an outer supporting metal casing 6.

The crucible, which is shown in a first normal upright position, has a pouring spout 8 provided at its upper end, so that no discharge of molten metal is possible from the crucible when it is in this first position.

The crucible is supported for tilting by means of a supporting frame 10 including two stub axles 12 which lie on a sequential plane of the crucible and about which the crucible can be tilted to a second pouring position permitting discharge of metal from the spout 8. The bearings which form a support for the stub axles and the means for tilting the crucible about these axles, are well known in the art and are not shown or described.

A substantially U-shaped duct 14 having a refractory wall extends from the base of the crucible and has its two ends communicating with the inside of the crucible respectively at two spaced apart regions. The duct is formed by three

separate parts

16, 18 and 20, each comprising an outer sheath of non-magnetic metal tube 22 having a refractory lining. This lining comprises an outer layer 24 of refractory material which is rammed or cast between the inner surface of the tube 22 and an inner layer 26 which is a pre-fired tube of refractory material. The adjacent cooperating ends of the

parts

16, 18 and 20 are mitered, so that the end faces of the linings in the tubes can firmly abut one another to ensure that no leakage of molten metal can occur from the duct at the joints between the parts. The ends of the tubes 22 have outwardly extending flanges such as 23, to enable the parts to be secured to one another and to the crucible. The flanges may be held together by any suitable means such as quickly detachable clamps (not detailed) which enable the joints between the'flanges to be easily and quickly released, so that any one or all of the parts may be replaced rapidly when the lining of the duct becomes excessively eroded.

A closed annular magnetic core 30, which surrounds one limb of the duct 14 formed by the part 16, is overwound by a winding 32 connectible to a suitable alternating current source. The winding 32 and the core 39 are arranged so that in use of the crucible, the winding is inductively coupled to the closed electrically conducting turn formed by molten metal in the duct 14 and molten metal in the body portion of the crucible. By this means, when the winding is energised to a suitable power level, the metal in the duct and thereby the metal in the crucible becomes induction heated and may be maintained at the desired temperature by suitable adjustment of the level of excitation of the winding. The winding 32 and the core 30 are supported on a framework 34 secured to the crucible independently of the duct, so that any or all the parts of the duct can be replaced without disturbing or interfering with the induction heating assembly.

In order to prevent the outer metal sheathing of the parts of the duct, with the crucible casing, forming a closed electrically conducting turn, an electrically insulating link is introduced at the joint between at least one 3 pair of co-operating flanges. This link may be in the form of a shim of a suitable electrically insulating material.

In use of conventional crucibles and in the case of certain metals, notably aluminium, it is believed that the oxides in the melt are increased as a result of a region of low pressure which exists at that region of the melt in the duct having a high coupling factor to the induction heating winding and which is produced by a constriction of the melt flow area in that region by the induced currents. This effect, known as the pinch effect, normally tends to draw air through the porous refractory material of the duct. The use of an outer metal sheathing tube for the duct, in the crucible described, produces an air impermeable layer which inhibits the ingress of air into the melt.

Since the refractory material of the duct merely forms a lining for, and is supported by, the outer metal sheath 22, the quantity of refractory material used in the

parts

16, 18 and 20 can be reduced to a minimum.

In the case where the crucible is to be used in conjunction with metal displaying a particularly high penetration into the refractory material used, cooling of the cold face of the lining of the

parts

16, 18 or 20 may be necessary. Accordingly, as shown in FIGURE 1, a convoluted metal tube 36, which is connectible to a source of cooling fluid, is welded or brazed to the outer surface of the metal tube 22 and is effective to cool the refractory lining of the

parts

16, 18 and 20 in use of the crucible. Although the parts of the duct have been described as being connected together by flanges on the outer metal tubes, it is to be understood that any means for securing the parts together, so that they can easily be dismantled, can be'employed. The parts may for example have cooperating stepped ends and may be spigotted together.

To form a good liquid metal seal at the joints between the ends of the parts, a suitable refractory cement may be employed at the joints.

The refractory material of the duct may be selected from a wide variety of inert refractory ceramics which are available as pre-fired tubes or as monolithic linings, rammed or cast in place. Thus the crucible may be used in conjunction with steel, nickel chromium alloys or other difficult charges by a suitable choice of refractory material.

The outer layer of refractory material may be a suitable packed monolithic refractory material. Thus it can be particulate and fluidic in nature and able to flow sufficiently to seal in use cracks which form in the inner pre-fired refractory layer.

Kit is desired to use a monolithic material for the inner refractory lining, one suitable method of providing it is ram or cast the material for the lining about'withdrawable,collapsible or fusible formers. For example, if for any particular application the necessary refractory for the duct lining is not available as a pre-fixed tube, the unfired material can be rammed into the metal sheath around a tubular metal former which in use of the crucible will be heated by induction, so firing the lining in place at the time of filling with the first charge of metal.

A very important feature of the present invention lies in the rapidity with which the induction heating duct can be replaced. By the use of quickly detachable clamps, and by the use of spigotted guides to lead the duct assembly quickly into the'correct position, very rapid duct repairs and/or replacement can be effected. It will be appreciated that the significant period is that between metal being emptied from the crucible and its being refilled with molten metal. Metal tight joints must be made between the hotscrucible body and the ends of the duct, suitably by a micanite gasket covered on each side with a refractory cement, and it is important that the duct shall be clamped to the crucible body sufficiently quickly for the clamping pressure to be fully applied before the cement cures. The time taken between metal being emptied and the crucible being refilled after repair or replacement of the duct can with a proper working system be brought down to 20 minutes or even 15 minutes.

The relining of the duct itself can also be effected relatively quickly, for example in one or two hours, the existing refractory lining being discarded and the metal sheath being reused.

What I claim is:

1. A refractory vessel suitable for containing a charge of molten metal comprising:

(a) a main body portion capable of holding a substantial part of the charge;

(b) a normally lower end to the body portion;

(c) induction heating means including an annular magnetic core; a i

(d) a duct threading the annular core and having first and second ends;

(e) a metal sheath forming an outer part of the duct;

(f) a refractory lining forming an inner part of the duct and disposed inside the metal sheath; and

(g) clamping means by which the duct is releasably secured to the normally lower ends of the duct in communication with the inside of the body portion; whereby the duct can be removed and replaced without dismantling the induction heating means.

2. A refractory vessel according to claim 1, in which the outer metal sheath is of non-magnetic metal.

3. A refractory vessel according to claim 1, in which the vessel includes a metal body, the duct is secured to the metal body, and the connection between the duct and the metal body is such that there is no electrically continuous path along the duct through the metal sheath and through themetal body of the vessel.

4. A refractory vessel according to claim 1, in which the refractory lining comprises an inner pre-fired refractory layer arranged in use to contact molten metal in the duct, and an outer layer of a suitable packed monolithic refractory material in contact with the metal sheath.

5. A refractory vessel according to claim 4, in which the inner layer is a pre-fired refractory tube.

6. A refractory vessel according to claim 5, in which the outer layer is particulate and fluidic in nature and able to flow sufficiently to seal in use cracks which may form in the inner pre-fired refractory layer.

7. A refractory vessel according to claim 1, in which the inner refractory lining is of monolithic material.

8. A refractory vessel according to claim 1, in which cooling ducts are secured to the metal sheath in good thermal conductivity therewith.

9. A refractory vessel according to claim 8, in which the cooling ducts are arranged to convey cooling water.

10. A refractory vessel suitable for containing a charge of molten metal comprising:

(a) a main body portion capable of holding substantially the whole of the charge when the vessel is in a normal upright position;

(b) a normally lower end to the body portion;

(c) induction heating means including an annular magnetic core;

(d) a duct threading the annular core and having first and second ends;

(e) a plurality of duct parts assembled together to form different parts of the length of the duct;

(f) a plurality of metal sheaths each forming an outer part of one of the duct parts;

(g) a plurality of refractory linings each forming an inner part of one of the duct parts and disposed within one of the metal sheaths; and

(h) clamping means by which the parts of the duct are releasably secured to the normally lower end of the body portion with thefirst and second ends of the duct in communication with the inside of the body portion; whereby the duct parts can be removed and 5 replaced without dismantling the induction heating means.

11. A refractory vessel accordng to claim 10, in which each outer metal sheath is of non-magnetic metal.

12. A refractory vessel according to claim 10, in which the vessel includes a metal body, the duct is secured to the metal body, and the duct parts are so connected together and to the metal body that there is no electrically continuous path along the duct through the metal sheaths and through the metal body of the vessel.

13. A refractory vessel according to claim 10, in which the refractory lining comprises an inner pre-fired refractory layer arranged in use to contact molten metal in the duct, and an outer layer of a suitable packed monolithic refractory material in contact with the metal sheath.

14. A refractory vessel according to claim .13, in which the inner layer is a pre-fired refractory tube.

15. A refractory vessel according to claim 13, in which the outer layer is particulate and fluidic in nature and able to flow sufiiciently to seal in use cracks which may form in the inner pre-fired refractory layer.

References Cited UNITED STATES PATENTS 2,423,912 7/1947 Tama et al. -3 13-29 2,939,899 6/1960 Edstrand et al. 13-29 X 3,249,676 5/1966 Rydinger et al 13-30 X 3,334,171 8/1967 Fredrikson et al. 13-29 RICHARD M. WOOD, Primary Examiner.

US. Cl. X.R. 1329